public virtual IDisposable Subscribe(IObserver <T> observer)
{
var factory = new Lazy <PropertyChangedEventHandler>(() =>
{
PropertyChangedEventHandler handler = (s, e) =>
{
if (e.PropertyName == PropertyName)
{
observer.OnNext(GetValue());
}
};
Source.PropertyChanged += handler;
return(handler);
});
PropertyChangedEventHandler handler = Observers.GetOrAdd(observer, _ => factory.Value);
return(Disposable.Create(() => Source.PropertyChanged -= handler));
}